1. Field of the Invention
The present invention relates to an optical scanner and an image forming device using the optical scanner.
2. Description of the Related Art
An image forming device such as a copier, a printer and a facsimile, which forms an electrostatic latent image onto an electrostatic latent image carrier by irradiating the electrostatic latent image carrier while deflecting laser light according to image information, and forms an image by developing the electrostatic latent image, is known. An optical scanner which deflects laser light generally includes on an optical path from a light source to a surface of an electrostatic latent image carrier of a light irradiation target an aperture stop, a cylindrical lens, a rotation deflector (polygon scanner) having a rotary polygon mirror, various mirrors and the like. The aperture stop, the cylindrical lens, the rotation deflector and various mirrors are housed in an optical housing.
The cylindrical lens as a condensing lens condenses in the sub-scanning direction laser light shaped by the aperture stop, and controls the light volume and the beam spot diameter in the sub-scanning direction. The beam spot diameter of the cylindrical lens is increased by attachment errors relative to an axis parallel to an optical axis, attachment errors in the sub-scanning direction and attachment errors relative to an axis parallel to the main-scanning direction. For this reason, it is important for the cylindrical lens to be appropriately positioned in and attached to the optical housing.
JP2007-47765A describes an optical scanner having a positioning member for positioning a cylindrical lens and a fastener for fastening the cylindrical lens to the positing member by pressing the cylindrical lens to a positioning portion of the positioning member. In the optical scanner described in JP2007-47765A, the positioning member to which the cylindrical lens is fastened is fastened to a base of the optical housing, and the fastener is attached to the positioning member by hitching the fastener to a hitching portion provided in the positioning member.
In JP2007-47765A, however, the positioning member is fastened to the base of the optical housing, so that the cylindrical lens may not be appropriately positioned relative to the optical housing by the attachment errors between the positioning member and the base. Consequently, the present inventors have developed the following optical scanner. More particularly, a positioning portion in which a cylindrical lens is positioned is directly mounted on the optical housing, and the cylindrical lens is fastened by pressing the cylindrical lens to the positioning portion by means of a fastener. The fastener is attached to a fastener attachment portion of the optical housing provided in the upstream side of the cylindrical lens in the light traveling direction. As described above, since the cylindrical lens is positioned by using the positioning portion directly mounted on the optical housing, without using the positioning member which is not directly mounted on the optical housing, attachment errors between the positioning portion and the optical housing do not occur. Therefore, the positioning accuracy of the cylindrical lens can be improved compared to the optical scanner described in JP2007-47765A.
As described in JP2007-47765A, when the fastener is fastened to the hitching portion provided in the fastener attachment portion of the housing, loosening of the fastening of the fastener occurs if the optical scanner vibrates, and the position of the cylindrical lens may be changed. For this reason, in the optical scanner under development, the fastener is threadably mounted on the fastener attachment portion of the housing. When fastening the fastener to the fastener attachment portion, an attached plane extending in the light traveling direction and having a screw insert hole is mounted on the fastener. A screw is inserted into the screw insert hole of the attached plane, and then the screw is screwed into a screw hole provided in the fastener attachment portion of the optical housing, so that the attached plane of the fastener is attached to the fastener attachment portion of the optical housing. As a result, the length of the fastener attachment portion to which the attached plane of the fastener extending in the light traveling direction is attached is increased in the light traveling direction.
In order to downsize an image forming device, it is necessary to downsize the optical scanner under development in the light traveling direction. In order to condense laser light in a predetermined spot diameter on an electrostatic latent image carrier by a cylindrical lens, it is necessary to obtain a predetermined length of an optical path from the cylindrical lens to the electrostatic latent image carrier. For this reason, it is necessary to downsize the optical scanner in the light traveling direction while obtaining the optical path length from the cylindrical lens to the electrostatic latent image carrier which can obtain a predetermined beam spot diameter.